Optical burst switching can be used in either an unbounded optical medium format or a bounded optical medium format. An unbounded optical medium is one where an arbitrarily mesh interconnected set of optical cross connects provide a fibre transmission path infrastructure through which optical bursts are propagated between sources and destinations distributed throughout the mesh.
In a bounded optical medium format, the optical transmission infrastructure is closed to provide a constrained transmission path, normally a fibre ring, across which direct connectivity is possible between sources and destinations with no intermediate optical cross connection being required. In the former unbounded case optical bursts must be routed through the mesh of optical paths, and scheduled to ensure bursts do not collide at any point in the network. In the latter bounded case bursts need only be scheduled, as the route is a straight propagation along a single transmission medium shared between all sources and all destinations.
This invention is concerned with the bounded optical burst switching system format. In this a series of source destination pairs are provided access to drop and insert optical bursts from and to a shared optical transmission medium. An example of this is provided by connecting a set of optical burst source destination pairs together using a single continuous fibre ring with tap points providing the drop and insert points for each pair. This arrangement provides a means by which any source may transmit to any destination. Each source must precisely time its burst transmission at each optical channel to ensure it will not interfere or collide with any source attempting to transmit on the same optical channel. The optical channels are defined by the wavelength used for optical transmission. Scheduling is used to ensure no collisions take place and to ensure that each source on the system has fair access through the optical transmission medium to each destination, and that each destination is given fair connectivity through the optical transmission medium to each source.
The system also provides a means by which incoming service flows are queued then transmitted across the medium each to its respective destination. Multiplexed service flows may be presented at a source, so the service management aspect of the system de multiplexes these and then multiplexes them into queues for transmission to the correct destination. The scheduling system removes the service queued information and transmits this in burst format across the medium to its destination port on the system.
When the incoming service flows are ethernet, the optical burst switch system provides a distributed ethernet switch. With legacy ethernet switching technology a network is created by interconnecting ethernet switches using optical transport technology. Here the switching nodes provide some client ports while other ports are reserved for interconnecting switching nodes. A problem with this arrangement is that the network owner must separately engineer the switching layer of the network from the transport layer of the network. The distributed ethernet switch overcomes this by using the optical burst switching layer as both a transport layer and switching fabric. This simplification provides a carrier with frame level direct optical forwarding between the ports around the closed fibre medium. The number of switching stages are also minimised using such a distributed switch system, which reduces the inherent latency through the network and simplifies the control plane over head required to provision and manage flows through the network.
However a drawback of the optical burst switching based distributed switch is that the burst medium is closed and therefore inherently limited in capacity. The capacity of the system is set by the transmission bit rate of the optical source modulator and the number of optical channels that can be supported. For example a 10 Gb/s optical line rate with 80 possible active wavelengths will nominally scale to 800 Gb/s. The nominal capacity is not completely achievable as the optical burst switching system with real time scheduling will exhibit a fabric efficiency of around 83%. Higher scaled networks can be created by interconnecting distributed ethernet switches over fixed optical connections, but while this reduces the number of switching stages in comparison with legacy switches interconnected by fixed optical lines, it still carries the burden of control plane management and multiple hops for individual frames.
Ultimately therefore the distributed ethernet switch built from an optical burst switching system is limited in scale by the fact that bursts cannot extend outside the closed optical medium. Unbounded optical burst switching systems are able to scale too much larger theoretical limits, but are difficult to build commercially. While the bounded optical burst system is practically viable, it has limitations in scale set by the spectral efficiency possible over the closed medium.
PCT patent publication number WO2005034569A2, assigned to Intel Corporation, discloses an optical switched network using extended Border Gateway Protocol (BGP). The PCT patent publication describes a modification to the Border Gateway Protocol (BGP) in order to allow IP routing header information from within an Optical Burst Switching (OBS), referred to therein as a Photonic Burst Switched (PBS) open network, to be used to route traffic through open OBS network zones in conjunction with other routing zones such a enterprise LAN and WAN networks. To do this the IP header information is taken from the traffic path at the border between two OBS zones, or an OBS zone and a non OBS zone, and the routing protocol is used to determine where to send the traffic in each zone accordingly. The system allows for the creation of extensions to BGP that allow traffic to be routed between PBS (OBS) fabrics. However a problem with this system is that it is restricted to IP addressing and cannot route data from multiple service providers on the same network.
A second PCT publication number WO2005/062578, assigned to Intel Corporation, discloses an architecture for optical networking between server and storage area networks. This system attempts to encapsulate fibre channel frames into one or more OBS data bursts. To create a networking solution with this, the routing protocols must use the fibre channel addresses, or the PBS addresses to provide routes through the group of PBS and non PBS fabrics. The control plane for such a group of fabrics must therefore be service specific, in this case fibre channel, but in the general case comprised of the addressing scheme of the client service, or PBS (OBS) specific, where the OBS system is therefore pre-connected to provide a transport server for the client service network.
It is an object of the invention to provide an optical burst switching system and method of scaling beyond the limitation set by the optical channel density and the optical line rate within the closed optical layer.